After an enabling end (EN) of an IC chip receives an input power, an initialization process is performed in the IC chip. After the initialization process is completed, an internal trigger level (namely an enabling level) becomes a high level, and the IC chip accordingly starts normal operation. During normal operation of the IC chip, if the voltage of the input power is instable and fluctuates, the level of the enabling end EN may be pulled down, so that the IC chip stops operating.